1. Field of the Disclosure
This disclosure generally relates to a sensing device and, more particularly, to a concurrent driving capacitive touch sensing device capable of resending drive signals.
2. Description of the Related Art
Capacitive sensors generally include a pair of electrodes configured to sense a finger. When a finger is present, the amount of charge transfer between the pair of electrodes can be changed so that it is able to detect whether a finger is present or not according to a voltage variation. It is able to form a sensing matrix by arranging a plurality of electrode pairs in matrix.
FIGS. 1A and 1B show schematic diagrams of the conventional capacitive sensor which includes a first electrode 91, a second electrode 92, a drive circuit 93 and a detection circuit 94. The drive circuit 93 is configured to input a drive signal to the first electrode 91. Electric field can be produced between the first electrode 91 and the second electrode 92 so as to transfer charges to the second electrode 92. The detection circuit 94 is configured to detect the amount of charge transfer to the second electrode 92.
When a finger is present, e.g. shown by an equivalent circuit 8, the finger may disturb the electric field between the first electrode 91 and the second electrode 92 so that the amount of charge transfer is reduced. The detection circuit 94 can detect a voltage variation to accordingly identify the presence of the finger.
Principles of the conventional active capacitive sensor may be referred to U.S. Patent Publication No. 2010/0096193 and U.S. Pat. No. 6,452,514.
Referring to FIG. 1C, the detection circuit 94 generally includes a detection switch 941 and a detection unit 942, wherein the detection unit 942 can detect a voltage value on the second electrode 92 only within the on-period of the detection switch 941. However, signal lines of the sensing matrix in different touch panels can have different capacitances, and the drive signal inputted by the drive circuit 93 can have different phase shifts corresponding to different sensing matrices. Therefore, the on-state of the detection switch 941 has to be adjusted corresponding to different touch panels or it is not able to detect correct voltage values. And this adjustment process can increase the manufacturing complexity.
In addition, when the capacitive sensor is applied to some systems (e.g. the liquid crystal display system), serious noise problems may exist. Accordingly, how to suppress the noise is also an important issue of this field.